ABSTRACT
Dihalodiboranes(4) react with a N-heterocyclic silylene (NHSi) to generate NHSi adducts of 1-aryl-2-silyl-1,2-diboraindanes, as was confirmed by X-ray crystallography, featuring the functionalization of both B-X (X=halogen) bonds and a sp3 - or sp2 -C-H bond under mild conditions. Coordination of a third NHSi to the proposed 1,1-diaryl-2,2-disilyldiborane(4) intermediates, generated by a twofold B-X insertion, may be crucial for the C-H borylation that leads to the final products. Notably, our results demonstrate the first C-H borylation with a strong B-F bond activated by silylene insertion.
ABSTRACT
A commercial phosphorus-based reagent (P(NMe2)3) mediates umpolung alkylation of methyl aroylformates with benzylic and allylic bromides, leading to either Barbier-type addition or ylide-free olefination products upon workup. The reaction sequence is initiated by a two-electron redox addition of the tricoordinate phosphorus reagent with an α-keto ester compound (Kukhtin-Ramirez addition). A mechanistic rationale is offered for the chemoselectivity upon which the success of this nonmetal mediated C-C bond forming strategy is based.
Subject(s)
Alkenes/chemistry , Organophosphorus Compounds/chemistry , Alkylation , Allyl Compounds/chemistry , Catalysis , Esters , Hydrocarbons, Brominated/chemical synthesis , Hydrocarbons, Brominated/chemistry , Magnetic Resonance Spectroscopy , Molecular Structure , Oxidation-Reduction , StereoisomerismABSTRACT
A reductive homocondensation of E-benzylidenepyruvate esters mediated by P(NMe2)3 is described. The transformation, initiated by the Kukhtin-Ramirez addition of the phosphorus reagent to the vinyl-substituted α-dicarbonyl substrate, proceeds via a resonance delocalized oxyphosphonium dienolate intermediate to provide access to diverse oxygenated heterocycles as a function of the substituent.
